PORTSMOUTH — The year-long residential real estate sales rally has left the supply of single family homes available for sale at its lowest level since at least 2010, according to the Seacoast Board of REALTORS monthly survey of the 13-sample Seacoast towns.

In June there were some 654 single family units available, but that number slipped to 377 last month. Still, condominium inventory actually grew a modest 7.2%.

For the month of December, residential sales declined 6.1% from a year ago, although sales for the year were up a whopping 29.9%.

The 23 condominium sales for December, all under $300,000, represent a 17.9% decline from 2011. But again, total volume for 2012 significantly exceeded 2011 by 30%.

While the decline in inventory would seem to favor an appreciation scenario, monthly numbers reveal no clear trend. The median price of a single family home remained almost the same as 2011 for the year $328,000 vs $325,000.

Similarly the average condominium price for the year of $248,716 was nearly identical to last year’s $249,624.

“The facts are in: 2012 was an excellent time to buy and many Seacoast residents did just that and are enjoying their new homes today,” said Jim Lee, president of the Seacoast Board of REALTORS.

“With continuing record low interest rates and a still plentiful supply of homes to choose from, 2013 looks to be an excellent time to buy (or sell) as well. “